1981 CB750C Engine Rebuild Random Questions

baldjeff

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Hi all, if you've seen my other posts you know I started with inconsistent compression across all 4 cylinders. AMC kindly advised to adjust my clearances but digging a little deeper I found a leak in my cylinder 1 exhaust valves. I did a leak down test which confirmed that suspicion. So in addition to adjusting the clearances I figured I would address some other items at the same time. Since I'm going deeper I figured I may as well just do the rings while I'm at it. I also found both tensioners desperately need to be replaced. They're both cracking already at 30k miles. First random question, do I need to change the cam chain guides as well? They're both very hard, is the bigger middle one rubber or plastic? I can't tell if its just old solidified rubber or what. I think the top one is metal right? Also, are there any other items that might go overlooked which I should address while here? I'm definitely changing all the rubber bits, any dowels that aren't perfect, checking the lifters and polishing the camshafts. What about the oil pump? It's fully operational but I know there's o-rings in there, do they need to be replaced by now? Is it necessary to also change the crankcase tensioner if the other tensioners are in rough shape? Is it worth doing the bottom end since I'm already here? Any other advice? Responses are greatly appreciated!
 

amc49

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Rings only and even they are likely good for a while yet. The problem is that a teardown is destructive in nature and rings VERY easy to damage doing one.

You MUST take an investment in heavy duty quart freezer baggies as the parts must all go back in the exact same places or you create a nightmare of mis-matched parts. Mark the bags up with locations. Hope you like doing 1000 piece puzzles.

The 'rubber' on guides and tensioners is very hard and close to a plastic and that hard even new. Guides change based on wear, it's the tensioners that break quick when the hard rubber does not flex but so far and heat gets to them. Metal backed rubberized parts.

Factory service manual here for free, enroll and in the technical documents section............

http://www.cb750c.com/modules.php?name=Your_Account&redirect=viewtopic&t=301
 

baldjeff

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Yes, having read lots of your previous posts I have been super diligent about organization. I have a couple of 8 section bins already labeled for the valve pieces and I have the lifters and shims bagged up, all with labels. I have tons of pics and I have all the nuts and bolts in cardboard so I know exactly which hole they each came out of. Do you have any advice on cleaning everything? Can pistons and valves go in the ultrasonic cleaner? I've seen great results on youtube from attaching the valves to a drill and using scotch brite to clean them but that seems so harsh. Is that safe? Any advice on lapping? I'm definitely going to do it by hand but are there any things to keep in mind or tricks you can pass on?Any advice on cleaning threads without a tap and die kit? Thanks!
 
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